Thermionic amplifier



Sept. 20, 1932.

H. A. WHEELER THEHMIONI C AMPLIFIER Filed Aug. 17, 1929 NTOR ll. ,4. Wh s/er ATTORNEYS Patented Sept. 20, 1932 UNITED STATES PATENT OFFICE HAROLD A. WHEELER, 0]? GREAT NECK, NEW YORK, ASSIGNOR TO HAZELTINE CORPO- RATION, A CORPORATION 01' DELAWARE 'I'HERMIONIC AMPLIFIER Application filed August 17, 1929, Serial 110. 888,544, and in England July 8, 1980.

This invention relates to electric wave repeating apparatus and more especially to thermionic amplifiers adapted principally for amplifying electrical waves in the ardio-fre uency range.

An 0 ject of the invention is to provide an amplifier of the ty e specified which while utilizing no biasing attery or initial negative biasing potential on the control circuits, or grids, of the amplifier tubes is nevertheless adapted to provide a high degree of substantially distortionless amplification at lar volume levels.

fi further object is to provide an amplifier of the type specified having a low output impedance and which requires a relatively low space current su ply source for the anode circuit of the amplifier tubes resultant upon the omission of the permanent biasing potential from the-grids thereof.

The amplifier as disclosed herein requires a pair of vacuum tubes for each stage of amplification. Due to the particular manner in which these tubes are interconnected, separate sources of cathode and anode current are in general required for the respective tubes. Accordingly, a further object of the invention is to provide an amplifier of the type specified wherein common sources of cathode and anode current may be utilized for supplying the tubes.

As a general proposition, one of the essential requisites to distortionless amplificationby means of thermionic amplifiers, particularly at the higher energy levels, consists in the provision of a suflicient permanent negative biasin potential on t e grids of the tubes to maintain the grids at all times negative during signal reception. The effect of the impressed signaling current carrying the rid positive during a portion of each cycle is to permit the flow of grid current in the input circuit during such intervals which causes a potential drop therein and thus correspondingly reduces the signaling voltage applied to the tubes which results in distortion and limitation of output.

Even where the tgrids of the tubes are maintained suflicien y negative by a biasin potential, distortion is in general introduced into the repeated signal due to the non-linear grid voltage-plate current characteristic of the amplifier tubes. As a result of this fac tor the positive portions of the impressed signal are amplified to a greater extent than the negative for the reason that the tube works over a different portion of its voltageplate current characteristic when repeating the positive than when repeating the negative portions of the wave.

The present invention provides an amplifier which while dispensing with the initial or permanent negative biasing potential on the grids, eliminates the objectionable effects due to the grids being carried positive by the signaling waves. In addition, the operation of the amplifier is such that the same portion of the grid voltage-plate current characteristic of the tubes is utilized for amplifying both the positive and negative portions of the impressed signaling waves which, of course, reduces to a minimum, distortion due to the non-linearity of such' characteristic.

The above unique results are obtained by utilizing a pair of similar vacuum tubes for each amplifier stage. One terminal of an input circuit is connected directl to the cathode of one tube and thru a big impedance element, preferably a resistance, to the grid of the other tube. Correspondingly, the second input terminal is connected directly to the cathode of the second tube and thru a similar high impedance element to the grid of the first tube. Since the cathodes of the respective tubes are connected to opposite terminals of the input circuit the usual methods of supplying current to the cathodes and anodes thereof from common sources of supply would result in short-circuiting the input circuit. As a result, therefore, in eneral separate sources of supply are require and it' is necessary to couple the anode circuits of the tubes with the out ut circuit thru separate primary windings o a three winding transformer, the secondary of which is connected between the output terminals. The primary windings are so poled that the signaling waves repeated by the tubes produce additive effects in the output circuit.

Due to the opposite manner in which the tubes are connected to the input circuit, the grid of one tube will be carried positive by the impressed signaling wave at each instant 5 that the grid of the other tube is carried negative. Current will flow in the grid circuit of the tube having its grid positive, but this grid current will be limited to a very small value since it must flow thru the high impedance element connected to the corresponding 'd. As a result, the grid current will prouce an inappreciable voltage drop in the in ut circuit and will thus have a negligible efi ct in reducing the efl'ective signaling voltage applied to the in at sections of the tubes. Furthermore, since t e same amount of grid current will flow in the input section for both positive and negative portions of the si aling wave, there will be no distortion e ects due to unequal voltage drops in the input section for the positive and negative wave portions respectively.

As a result of the flow of grid current each tube is substantially inactive as regar repeating the signal during the intervals that the grid thereof is carried positive by the signaling wave. This is due to the fact that practically all of the signaling voltage impressed upon the input section of such tube is used up in overcoming the potential drop resultin from the flow of grid current thru the big impedance element. As a consequence, very little of the signaling voltage is applied between cathode and grid of the tube and hence such tube repeats the signal weakly to the output circuit. On the other hand, the tube having its grid carried negative by the signaling wave ofiers practically an open circuit impedance to the flow of grid current so that the full signaling voltage is applied directly between grid and cathode thereof, since none is lost in potential drop across the high impedance element, and accordingly such tube strongly repeats the signal. Thus each tube repeats signals only during the interval that its grid is maintained ne ative by the signaling wave with the result that both positive and negative portions thereof are amplified with the tubes working over the same portion of the grid voltage-plate current curve.

The arrangement for supplying the tubes from common cathode and anode sources is best explained by reference to the drawing of which:

Figure 1 shows the circuit diagram of an amplifier embodying the novel features of the present invention but using separate sources of cathode and anode current for the respective tubes.

Fig. 2 shows a modification of Fig. 1 wherein common potential sources of cathode and anodacurrent are utiliued for supplying all of the amplifier tubes. Fig. 2 shows further I ii an t whereby the circuits ance elements.

of the respective tubes are connected directly to a loud speaker of special construction.

The expression oppositely connected in parallel applied to the connection of the input circuits of the amplifier tubes, throughout the specification and claims designates the circuit arrangement illustrated in the drawing wherein the cathodes of the amplifier tubes are connected to the respective input terminals and the grid of each tube is connected through impedance means to the cathode of the o posite tube.

Re erring to Fig. 1, the amplifier com prises a air of similar vacuum tubes V and V each aving rid G, cathode or filament F, and an ode or p ate electrodes P. Separate batteries 1 and 3 are utilized to heat the filaments of tubes V and V respectively. The input circuits of the vacuum tubes are associated with a pair of input terminals I thru a transformer T having the primary P thereof connected directly to said terminals and having the upper terminal of the secondary winding S thereof connected directl to the ne ative terminal of the filament of tube 1 and connected thru a hi h resistance R to the grid of tube V S1milarly, the lower terminal ofsecondary S is connected directly to the negative terminal of the cathode of tube V and also thru a high resistance R to the grid of tube V The output circuit comprises a three-winding transformer T having a single secondary winding S: connected directly to a pair of output terminals O and a first primary windin P con- 1 nected from the plate of the'tube 1 thru a space supply source 2 to the cathode of the tube. A second primary winding P, is similarly connected from the plate of tube V thru a second space supply source 4 to the cathode of tube V The primary windings P and P are poled relatively so that the steady space supply currents flowing thru the res ctive windings produce opposing ma et1c fluxes in the transformer core.

e resistances R and R are, of course, similar in magnitude having a value of from .1 to 1.0 me ohm dependent upon the type of tubes use Any suitable high impedance elements traversable b uni-directional cur- 1 rent could be utilized 1n place of the resist- For example, choke coils would in some instances be well adapted to this purpose.

In the operation of the amplifier, when an incoming signaling wave is applied to the input terminals I in such manner that the upper terminal of S is negative relative to the lower terminal thereof, the grid of tube V will be carried positive and that of tube V, negative by the signaling voltage. Under such conditions, the current will flow from the u per terminal of S to the filament of tube 1 and thence thru the space path from filament to grid thereof, returning thru the Iii) - thereof, or vice versa.

resistance R and the windin S to the upper terminal of windin 8,. T e resistance R bein of large magnitude will, of course, limit the ow of rid current to a relativel small value, and urthermore due to the re atively small cathode-to-grid resistance of the tube compared to the resistance R practically the entire voltage of the impressed signal wave will be across the resistance and very little between the filament and grid of tube V The advantages of this combination of factors have been explained above.

On the other hand, the applied signaling wave being impressed between grid and filament of tube V in a negative sense, the impedance offered from grid to filament thereof amounts to practically an open circuit so that no current will flow in the series circuit comprising the winding S resistance R and the space path between grid and filament of tube V As a result, the entire voltage of the signal wave will be impressed between grid and filament of tube V which thus strongly repeats the signal in the primary winding P, of transformer T At the same time, tube V due to its positive bias, is weakly repeating the signal in the transformer winding P During the succeeding half cycle of the 'applied signaling wave, namely, while the lower terminal S is negative relating to the up er terminal thereof, the conditions descri ed above will be reversed so that current will flow in the grid circuit of tube V whereas no current will flow in that of tube V During this half cycle, therefore, tube V will strongly repeat the signal to the output circuit, and tube V will repeat the same to a practically negligible extent.

It will thus be seen that with the circuit arrangement described only one tube at atime is active in repeating the signal. Tube V1 for example, will repeat all the positive half cycles of the applied signal wave, whereas tube V will repeat all the negative half cycles The signaling wave flowing in the output circuit is therefore made up of half cycles for which each tube is always working over the same portion of its grid voltage-plate current characteristic, and hence, the repeated wave is substantially distortionless.

It is obvious from an inspection of Fig. 1 that the replacement of batteries 1 and 3, and 2 and 4 by common sources of potential would result in substantially short-circuiting the secondary winding of the transformer T since a conductive path would be formed between the terminals of the secondary winding S thru the common source of supply.

Fig. 2 shows an arrangement for utilizing common sources of cathode and anode supply without efl'ectively short-circuiting the input circuit to the amplifier tube.

Referring to Fig. 2, the input transformer T comprises a primary winding P, connected to the input terminals I and four similar secondary windings S to S inclusive, wound on the same core as primary winding P The secondary windings S to S, are so poled that a current active in the primary winding induces volta es in the various secondary windings in t e relative directions indicated by the arrows.

The secondar windings S and S, are serially connecte between the plates of tubes V and V respectively, over a circuit traced from the plate of tube V over lead 12 thru a winding 6 of a loud speaker unit L, over lead 11 thru the windings S and S in series, over lead 13, thru a second winding 7 of the loud speaker L and over lead 19 to the plate of tube V Windings S and S, are seriall connected between the midpoints of imped ance elements 1 and 2 brid ed across the cathodes of tubes V and Vi respectively. A common space current sup 1y source 17 for the anode circuits of the tu es is connected from a point between windings S and S, to a point between windings S and S The cathodes of tubes V and V are connected respectively to the secondary windings 15 and 16 of a transformer T having itsprimary winding connected to a pair of termi nals 14, whereby a common source of alternating current connected to terminals 14 will heat the filament of both tubes.

The grids of tubes V and V are connected thru resistance elements R and R to the outer terminals of windings S, and S respectively. The capacities C are brid ed across the outer terminals of windings 1 and S and S and 8,, respectively, to equalize the fluctuating currents flowing in the transformer windings, and thus prevent undesired reactions between the input and output circuits of the tubes and also to bypass the am lified signaling currents flowing in the ano e circuits of the tubes.

In the operation of the amplifier the space supply current for tube V considering now the true direction of current flow, flows from the negative terminal of battery 17 thru the winding S to the midpoint of impedance 1, whence it divides equally and flows in both directions to the filament F of tube V and thence in the space path to the plate P, returnin over lead 12, winding 6 of speaker L, lead 11, and thru the winding S to the positive terminal of the battery. It will be noted that the space current flowing in the circuit traced flows thru the windings S and S in such relative directions that the fluxes set up cancel one another so that the resultant flux due to the steady space current is zero. The space current for tube V flows ina similar manner from the negative terminal of battery 17 thru winding 5, to the midpoint of impedance element 2, whence it divides, flowin eipially in both directions to the filament 0 the tube and thence in the space path from filament to plate P thereof, return mg over lead 19 and thru winding 7 of speaker L, over lead 13 and thru the winding S to the positive terminal of battery 17. It will be noted that the current flows in windings S and S in such relative directions that the fluxes set up cancel each other.

Assuming now a signaling voltage to be impressed upon the in ut terminals I, the voltage induced in win ings S and S. Wlll be impressed in an additive sense upon the input sections of tubes V and V since these windings are serially connected thereacross. Assuming at a given instant the signaling voltage to be such that the upper terminal of winding S is negative relative to the lower terminal of windin 5., the grid of tube V will be carried positive and that of tube V negative by the signalin wave. As a result, current will flow in t e grid circuit of tube V which circuit is traced from the grid of tube V thru resistance element 3,, windings S4 and S in series to the midpoint of impedance 1 and thence in both directions to the filament of tube V, and back to the grid thru the space path of the tube, producing the effects pointed out above in connection with Fig. 1. Since the grid of tube V on the other hand, is carried negative by the impressed voltage, the full voltage of windings S and S in series is impressed between the grid and cathode of tube V thru the resistance element R and the impedance element 2. When the applied signaling voltage is such that the lower terminal of winding S, is negative relative to the upper terminal of winding S conditions will be reversed, the grid of tube V being carried negative and that of tube V positive by the signaling wave. It will thus be seen that the signaling voltages are impressed upon the amplifier tubes of Fig. 2 in the same manner as for the amplifier of Fig. 1.

Due to the relative polarities of windings S and S and windings S and S. a voltage active in the primary winding of transformer T produces no effect in the anode circuits of tubes V and V Considering the anod circuit of tube V if the voltage in the primary winding P is such as to produce a voltage in the direction indicated by the arrow in winding S it will produce an equal voltage in the direction indicated by the arrow in winding S and since the lower terminals of windings S and S are in effect short-circuited thru the battery 17, the voltages in the two windings will buck each other and thus set up no resultant current in the anode circuit of tube V In a similar manner, a current active in the primary windin P will produce no effect in the anode circuit of tube V; since, assuming the primary current to be such as toinduce a voltage in winding as indicated by the arrow, it will also induce an equal voltage iniwinding S, asindicated by its arrow, and these voltages will annul each other producin no resultant effect in the anode circuit 0 tube V,.

fied signaling current in the anode circuit of tube V however, which flows thru the secondary windings of the in ut transformer will flow in one direction t ru winding S and in the opposite direction thru winding S with the result that the fluxes will annul each other and induce no voltage in the primary winding P Similarl amplified signaling current flowing in t e anode circuit of tube V will flow in one direction thru winding S and in the opposite direction thru winding S producing zero resultant eflect upon primary winding P The connection of the input circuit to the cathodes of tubes V and V respectively, thru the midpoints of the impedance elements 1 and 2 prevents the grids from being affected by the alternating current sup ly utilized for heating the cathodes of the tu s and thereby eliminating any hum due to the cathode supply source.

In Fig. 2, the anode circuits of the tubes are connected respectively to a pair of signal current actuating windings of a special type of loud speaker unit known as the Farrand inductor dynamic speaker. The loud speaker L comprises a permanent horseshoe magnet 3 having aflixed to the inner surfaces of the poles thereof, respectively, a pair of U- shaped pole pieces 4 and 5 of soft iron or other easily magnetizable material. The pole pieces are so positioned that corresponding legs thereof are opposed leaving small air gaps therebetween in which is positioned a vertically movable armature 8 rigidly affixed by means of a rod 9 to the center of a. cone loud speaker unit 10. A signal current coil 6 is placed about the upper leg of pole piece 4 and a similar coil 7 is placed about the lower leg of pole piece 5. These coils are connected respectively in the anode circuits of tubes V and V as was explained above, being so poled that the steady space currents of the tubes flowing therethru in each case set up a flux in the same direction as that of the permanent magnet 3.

The armature 8 has a length slightly less than the distance between the outer surfaces of the pole piece legs, being positioned symmetrically in the air gaps and thus pulled equally in opposite vertical directions by the steady fluxes threading the upper and lower airgapabetweentheopposadlegaofthepole coil 7 remains constant at the normal direct current value or increases very little, because the grid of tube V is positive. Likewise, when the grid of tube V is positive, the current in signal coil 6 is practically at the normal direct current value and the current in signal coil 7 is decreased. From the foregoing it is seen that the signal coils are alternately operative and furthermore the coil which is inoperative exerts no influence upon the coil which is operative. This gives the result that the inactive tube of low plate resistance is not effectively a shunt across the output of the active tube, as would be true if a single output transformer were utilized.

The principal advantage of connecting the inductor type loud speaker directly in the anode circuits of the amplifier tubes is that all of the frequencies operate on the speaker unit to equal advantage, whereas if the speaker were connected to the terminals of an output transformer, as for example terminals O of Fig. 1, the lower frequencies would in general be discriminated against. Another advantage of the arrangement of Fig. 2 lies in the elimination of the output transformer T which represents an economy of construction. The greatest distor- 7 tionless power output is secured when there is practically no mutual magnetic coupling between coils 6 and 7 and when the efiective impedance of each coil is approximately three times the output impedance of the vacuum tubes individually connected thereto.

Referring back for a moment to Fig. 1, where signals varying in intensity from weak to strong are apt to be received, the distortionless operation of the amplifier is improved by making the resistances R and R, equal to the dynamic grid-filament impedances of the corresponding tubes measured at such weak intensities. For small impressed voltages, the cathode to grid resists ances of the tubes are very large, so that both tubes are about equally active at each instant in amplifying the impressed signal waves. At hi h intensities, however, the cathode to gri tube resistances drop to a relatively low value so that the resistances R and R become large in com arison and the operation is that described a ove wherein the tube having its grid carried positive by the signalling wave is substantially inactive in repeating the signal.

It thus results that with the above pro portioning of the elements R and R a substantially constant degree of amplification is obtained at all signal intensities- At low intensities one-half'the impressed signal voltage is at each instant im ressed between id and filament of each tu e and since both tubes are active at all times, in repeating such si nals the same degree of amplification is obtained as at high intensities where the full signaling volta e is applied at each instant to only one tu e, the other tube being substantially inactive.

What is claimed is:

1. In an amplifying system for electric waves, a pair of thermionic valves each including an input section, means connecting said input sections in parallel to a pair of input terminals but in a reversed sense relatively, said means comprising high impedance elements connected between said terminals and said input sections adapted to causesignal waves present in said input sections to be impressed in substantial entirety upon the valve which momentarily receives a negative potentialtherefrom, whereby said-latter valve alone repeats the signal.

2. In a thermionic amplifyinglsystem for electric waves for providing a igh de cc of substantially distortionless ampli cation in the absence of permanent biasing potentials in the control circuits of the thermionic elements, apair of thermionic valves each having a substantially unilateral input section, means connecting said input sections in a reversed sense relatively between a pair of input terminals, said means comprising high resistance elements connected between said terminals and said input sections, adapted to cause signal waves present in said 1nput sections to be repeated in substantial entirety by the valve which receives a negative potential therefrom, whereby said latter valve alone re eats the signal.

3. In an amplifying system in combination, a pair of thermionic valves each having an input section including grid and cathode, means connecting said input sections in parallel in a reversed sense relatively to a air of input terminals, and means included in each said input section for substantially prevent-' ing the flow of grid current therein, said means comprising high impedance elements connected between said terminals and said input sections, adapted to cause signal waves present in said input sections to be repeated in substantial entirety by the valve which receives a negative potential therefrom, whereby said latter device alone re eats the signal.

4. In a thermionic amp ifying system, for roviding a high degree at substantially distortionless amplification in the absence of biasing potentials in the control circuits of the thermionic elements, a pair of thermionic valves each having an input section including a grid and a cathode, means connecting said input sections in a reversed manner relatively between a. air of input terminals, and means include in Said input sections efi'eotive to limit to a small value the positive potential of said grids but inefi'ective to limit the negative potential thereof due to signal voltages applied between said input terminals, said means comrising high resistance elements connected etween said terminals and said input sections ada ted to cause said signal waves to be impresse in substantial entirety upon the valve which receives a negative otential therefrom, whereby said latter va ve alone repeats the signal.

.5. In a thermionic amplifying system, for providing a high degree of substantially distortionless amplification in the absence of negative biasing potentials in the control circuits of the thermionic elements, a, pair of thermionic valves each having an input section includin a grid and a cathode, means connecting said input sections in parallel in 0 a reversed manner relatively between a pair of input terminals, hi h impedance means serially included in sai input sections operative to limit to a small value the positive potential of said grids but inefi'ective to limit the negative potential thereof due to signal voltages a lied between said input terminals, sai high impedance means comprising a air of fixed high im edance elements one of which is connected etween the first of said input terminals and the control electrode of the second of said valves and the other of which is connected between the second of said input terminals and the control electrode of the first of said valves, the cathode of said first valve being connected to said first input terminal and the cathode of said second valve being connected to said second input terminal, whereb one tube repeats positive and the other tu negative portions of electric waves impressed between said terminals.

6. In a thermionic amplifying s stem for providing a high degree of su stan- I tially distortionless amplification in the absence of biasing potentials in the control circuits of the thermionic elements, a pair of thermionic tubes each having an input section including grid and cathode, means connecting the grid of one tube and the cathode of the other to one input terminal, means similarly connecting the cathode of the first tube and grid of the second tube to a second input terminal, said means including a high impedance element in series with each said grid, said im edance elements being of fixed magnitude a apted to cause a signal wave applied between said in ut terminals to be impressed in substantia entireupon the tube whose grid receives a negam tive potential therefrom whereby one tube repeats positive portions and the other tube negative (portions of electric waves impressed upon sai in ut terminals.

7 An amp ifyin system comprising a pair of thermionic va ves each comprising an other of which is connected between the second of said input terminals and the control electrode of the first of said valves, the cathode of said first valve bein connected to said first input terminal and t e cathode of said second valve being connected to said second input terminal and means coupling said output sections in opposition to an output circuit. wherebv equal positive and negative voltages applied to said input circuit produce respectively equal positive and negative efiects in said output circuit.

8. In an amplifying system, a pair of thermionic valves each having an input section including a cathode and a control electrode, and an output section, means connecting said input sections in a reversed sense re atively between a pair of input terminals, the cathode of the first of said valves bein connected to the first of said terminals and the cathode of the second of said valves being connected to the second of said terminals, means coupling said output sections to an output circuit, and a high impedance element connecting each control electrode with the cathode of the opposite valve for causing a signal wave applied between said input terminals to be impressed in substantial entirety upon the input section of the tube whose grid receives. a negative potential 195 therefrom, whereby said latter valve alone repeats the signal.

9; An am lifying system comprising a pair of thermionic tubes each having an input section including grid and cathode, and an output section, means connectin said input sections oppositely in parallel tween a pair of input terminals whereby the grid of one tube is momentarily rendered positive and thegrid of the other tube simultaneously I15 rendered ne ative by a signal voltage impressed ther between, and means included in said input sections for rendering said tubes substantially inactive while their grids are positive, whereby electric waves impressed be- 150 tween said terminals are repeated at each instant by the tube having the negative grid.

10. An amplifying system comprising a pair of thermionic tubes each havi an input section including grid and cathode and an output section, means connecting sai input sections oppositely between a pair of input terminals whereby the grid of one tube is rendered positive and the grid of the other tube simultaneously rendered negative by e 9 Ill signal voltage ini ressed therebetween, means included in said input sections for rendering said tubes substantiallly inactive while their grids are positive, an means coupling said output sections in opposition to an output circuit, whereby equal positive and negative voltages applied to said input terminals produce equal positive and negative effects in said output circuit and whereby electric waves impressed upon said input terminals are regeated in said output circuit at each instant y the tube having the negative grid.

11. A thermionic amplifying system adapted to provide a high degree of substantially distortionless amplification in the absence of biasing potentials in the control circuits of the thermionic elements, comprising a pair of thermionic tubes each having an input section including grid and cathode, and an outputsection, means connecting the cathode of the first of said tubes to a first input terminal and the cathode of the second of said tubes to a second input terminal, a high resistance element connectin the cathode of the first of said tubes with t e grid of the second of said tubes and a similar high im edance clement interconnecting the remaining grid and cathode, means similarly connecting the grid of the second tube thru a resistance and the cathode of the first tube to a second input terminal and means connecting said output sections in opposition to an output circuit, whereby signal waves ap lied across said input terminals are impresse in substantial entirety upon the input section of the tube whose grid momentarily receives a negative potential therefrom, whereby said latter tube alone repeats the signal, and said signal waves are repeated in said output sections regardless of which tube is momentarily repeating the signal.

12. A thermionic electric wave repeating apparatus for providing a high degree of substantially distortionless amplification in the absence of biasing potentials in the control circuits of the thermionic elements, comprising a pair ofinput terminals, input and output circuits, a pair of vacuum tubes each including a cathode and grid, one of said cathodes being connected to one input terminal, the other of said cathodes being connected to the other input terminal. said grids being connected oppositely in said in ut circuit, means interposed between said grids and said input circuit for rendering one tube substantially unresponsive to positive portions and the other substantially unresponsive to negative portions of electric waves in said input circuit said means comprising a pair of resistance elements one of which is connected in series with each grid, the end of each resistance element remote from the grid being connected to the cathode of the other tube, whereby the negative portion of the wave is repeated by one tube and the positive portion by the other tube in said output section.

13. A thermionic amplifier comprising a pair of vacuum tubes each having an anode, cathode and grid, means connecting the rids thereof oppositely across a first impe ance means, means connecting said anodes respectively to opposite terminals of a second impedance means, and an anode supply source connected between intermediate points of said first and second impedancemeans, said impedance means being other and to an input section that electric waves active in said input section are effective upon said grid circuits but electric waves active in the anode circuits of said tubes are inefi'ective upon said input and grid circuits.

14. A thermionic amplifier comprising a pair of vacuum tubes having the grid circuits thereof connected oppositely across a first pair of serially connected windings and the anodes connected respectively to opposite terminals of a second pair of serially connected windings, and an anode supply source connected from a point between said first pair of windings to a point between said second pair of windings, sai windings being so coupled to each other and to an input circuit that electric waves active in said input circuit are effective upon said grid circuits but electric waves active in the anode circuits of said tubes are ineffective upon said input and grid circuits.

15. A thermionic amplifier comprising a pair of vacuum tubes having the grid circuits thereof connected oppositely across a first pair of serially connected windings and the anodes connected respectively to opposite terminals of a second pair of serially connected windings, an anode supply source connected from a point between said first pair of windings to a point between said second pair of windings, said windings being so coupled to each other and to an input circuit that electric waves active in said'input circuit are effective upon said grid circuits, but electric waves active in the anode circuits of said tubes are ineffective upon said input and grid circuits, and a capacity connected from each outer terminal of said first pair of windings to the corresponding outer terminals respectively of said second pair of windings.

16. A thermionic amplifier comprising a pair of vacuum tubes each havin anode, cathode and grid electrodes, means $01 heating said cathodes from a common source comprising a transformer having secondary windings individually connected to said cathodes respectively, impedance elements bridged between the terminals of each said cathode, a first pair of windings serially connected from an intermediate point of said first to an intermediate point of said second impedance element, a second pair of windings serially interposed between the ahodes of said tubes respectively, an anode supply so coupled to each.

source connected from a point between said first to a point between said second pair of windin means connecting the grid of each said tu thru an impedance to the cathode of the other tube, said windings being so coupled to each other and to an input circuit that electric waves active in said input circuit are effective upon the grid circuits of said tubes, but electric waves active in the m anode circuits thereof are inefiective upon said input and grid circuits, and means separately couplin the anode circuits of said tubes to a load 17. A thermionic amplifier comprising a pair of vacuum tubes each having anode, cathode and grid electrodes, means or heating said cathodes from a. common source including a transformer having secondary windings individuall connected to said cathodes, impedances ridging the terminals of each said cathode, an input transformer having a first secondary winding extending between intermediate points of said impedances respectively, and a second seconda winding connected between the anodes of said tubes respectively, an anode supply source connected between corresponding intermediate points of said second first and said secondary windin s, means connecting the grid of each tube t ru an impedance to the cathode of the opposite tube, said secondary windings being so coupled to each other and to a primary winding that electric waves active in said primary are efi'ective upon the 33 grid circuits of said tubes, but electric waves active in the anode circuits thereof are inefiective upon said rimary winding and said grid circuits, an output windin individual to the anode circuits of said tubes respectively, said output windings being magnetically coupled to a load.

18. The combination with a thermionic amplifier for rovidin a high degree of substantially istortio ess amplification in the absence of biasing potentials in the control circuits of the thermionic elements, comprising a pair of vacuum tubes each having an anode, a cathode and a control electrode and having thewgrid circuits thereofconnected oppositely to an input circuit, a'first high impe ance element connecting the cathode of one tube to the grid of the other tube and a second high im edance clement connecting the remaining grid and cathode and said cathodes bein connected ively to said input terminals whereby signalingwaves applied across said input terminals are impressed in substantial entirety upon the tube which receives a negative potential therefrom so that said latter tube re ate the signal of a loud speaker unit in uding means for producing a rmanent magnetic flux adapted to maintain in dynamic equilibrium an armature afixed to an acoustical unit, a pair of signal current coils for actuating said armature situated respectively adjacent opposite ends thereof, means so connecting said coils individuall in the anode circuits of said tubes respective y that the fluxes due to the space currents flowing in each case aid said permanent flux, whereas signal waves repeated by said tubes produce additive effects upon said armature at any instant, regardless 0 which tube is repeating the signal.

19. In a wave repeatin system, a pair of input terminals, a pair 0 output terminals a pair of impedance elements and a pair of repeating elements, each of which has an input circuit and an out ut circuit, the input circuit of one of sai repeating elements being arranged in series with one of said impedance elements, the input of the other of said repeating elements being arranged in series with the other of said impedance elements, said'series arrangements being connected in parallel in an opposite sense to said input terminals so that the ends of said im pedance elements remote from the associated input circuits are connected to opposite in ut terminals, whereby signal waves applied across said input terminals are impressed in substantial entirety upon the input circuit of the repeating element which receives a negative potential therefrom so that said latter repeating element repeats the signal.

20. In a thermionic wave repeating system for providing a bi h degree of substantially distortionless amp ification in the absence of negative biasing potentials in the control circuits of the thermionic elements, in combination, a pair of input terminals, a pair of impedance elements, and a pair of thermionic repeating elements, each of said regeatin elements comprising a cathode, arm 0 an grid, one of said impedance elements having one of its terminals connected to the first of said input terminals and its other terminal connected to the grid of the second of said repeating elements, the cathode of said second repeating element being connected to the sec 110 0nd of said input terminals, and the other of said impedance elements having one of its terminals connected to the second of said input terminals and its other terminal connected to the grid of the first of said repeat- 116 ing elements, the cathode of said first repeatin element being connected to the first of sa' input terminals, whereby si al waves applied across said input termin s .are im- 7 pressed in substantial entirety upon the re- 120 peating element whose grid receives a negative potential therefrom, so that said latter repeating element repeats the signal.

21. In a thermionic amplifying system for providing a high degree of substantially dis- 1% tortionless amplification in the absence of negative biasing potentials in thecontrol circuits of the thermionic elements, in combination, a pair of input terminals, a pair of high impedances and a pair of space discharge I pedances, the other terminal of the first of said impedances to the control electrode of the second of said devices, the cathode of the second of said devices to one terminal of the second of said impedances, the other terminal of the second of said impedances to the control electrode of the second of said devices one of said input terminals being connected to one cathode and the other input terminal to the other cathode, whereby signal waves applied across said input terminals are impressed in substantial entirety upon the device whose control electrode momentarily receives a negative potential therefrom, so that said latter device is alone eflective to repeat the'si l.

22. he combination of claim 21 in which said impedances are resistance elements.

In testimon whereof I aflix m si ture.

IAROLD A. E ER.

. Certificate of Correction Patent No.'1,878,742.

HAROLD A. WHEELER g'Itjs hereby certified that error appears in the rinted specification of the aboveage 1, hne 57, before voltagea; and same page, and that the said Letters Patent shook? be read with these the same may conform to the record of the case in the Patent numbered patent requiring correction as follows: ipsert the word page 2, line 53, for drawing read dmwin hne 89, for S, read 8y corrections therein that co. Signed andsealed this 29th day ofNovember, A. 1). 1932.

[ M. J. MOORE,

Acting Commissioner of Patmta September 20, 1982.

pedances, the other terminal of the first of said impedances to the control electrode of the second of said devices, the cathode of the second of said devices to one terminal of the second of said impedances, the other terminal of the second of said impedances to the control electrode of the second of said devices one of said input terminals being connected to one cathode and the other input terminal to the other cathode, whereby signal waves applied across said input terminals are impressed in substantial entirety upon the device whose control electrode momentarily receives a negative potential therefrom, so that said latter device is alone eflective to repeat the'si l.

22. he combination of claim 21 in which said impedances are resistance elements.

In testimon whereof I aflix m si ture.

IAROLD A. E ER.

. Certificate of Correction Patent No.'1,878,742.

HAROLD A. WHEELER g'Itjs hereby certified that error appears in the rinted specification of the aboveage 1, hne 57, before voltagea; and same page, and that the said Letters Patent shook? be read with these the same may conform to the record of the case in the Patent numbered patent requiring correction as follows: ipsert the word page 2, line 53, for drawing read dmwin hne 89, for S, read 8y corrections therein that co. Signed andsealed this 29th day ofNovember, A. 1). 1932.

[ M. J. MOORE,

Acting Commissioner of Patmta September 20, 1982. 

